Research in the Waves & Beams Division is divided into
four major areas:

In recent research, we have completed two major advances in
creating high quality output beams from gyrotrons. In a 1 MW, 110 GHz
gyrotron we have succeeded in creating an output beam, which is
nearly a perfect Gaussian beam the gyrotron efficiency is increased
and the design of auxiliary transmission line components is greatly
simplified. That work was carried out in collaboration
with Communication and Power
Industries of Palo Alto, CA and General Atomics of San Diego, CA.
In a second application, the same techniques have been applied to the
design of phase correcting mirrors for use on the LHD stellarator
experiment in Japan as part of an international collaboration program.
To extend this research to higher power levels needed in future
ERH experiments, we have initiated a study for a 1.5 MW, 110 GHz
gyrotron. A prototype gyrotron has been built and is being tested at
MIT to be followed by a CW gyrotron that will be built by industry.

A new idea for a gyrotron microwave window,
a dome shaped window capable of handling megawatt level CW power has
been demonstrated. This research is primarily sponsored by MIT Lincoln Lab through their
Advanced Concepts Committee (ACC) internal funding program. In
research on a 250 GHz gyrotron oscillator for use in
sensitivity-enhanced nuclear magnetic resonance through dynamic nuclear
polarization, successful operation was achieved at CW power levels of up
to 25 W. This research, funded by the NIH in collaboration with Prof.
Robert G. Griffin, Director of the Francis Bitter Magnet Laboratory, is a
pioneering effort in high field dynamic nuclear polarization
studies. Recently, a 460 GHz CW second harmonic gyrotron oscillator
developed for DNP studies has generated a record CW power level
of over 8 W.

We have completed a research program on
Innovative Vacuum Electronics, which was sponsored as an MURI consortium. We have successfully
demonstrated the operation of a novel 140 GHz gyrotron oscillator
with a highly overmoded interaction structure. A second harmonic
gyrotron oscillator experiment is currently in progress to demonstrate
the effectiveness of quasi-optical open resonators for mode
selective operation in gyrotron. We are also exploring alternative
ideas for interaction structures for high frequency (100-1000 GHz)
microwave tubes. We have demonstrated a new idea for building high
frequency microwave tubes with overmoded interaction structures made
of photonic band gap (PBG) structures. A proof-of-principle
experiment æ a novel gyrotron with a PBG resonator
was successfully operated in a very high order mode without mode
competition over a wide frequency bandwidth. We have begun research
on a gyrotron amplifier at 95 GHz. Initial experiments for the
amplifier are planned at 140 GHz and the device is being readied for
testing.

We are involved in normal conducting accelerator research at high frequency,
namely 17.14 GHz. With an available 25 MW of RF power we can run independant
experiments, such as RF guns, as well as experiments with beams on our 25 MeV
electron linac line.

We have demonstrated over 350 MV/m in an RF gun. We have demonstrated the first
accelerator structure with a Photonic Band Gap structure. We have demonstrated
bunch length measurements from Smith Purcell radiation observations. And we
have developed an electric field integral equation code in support of Smith
Purcell Radiation experiments, which has been verified through both Smith
Purcell and Coherent Transition radiation experiments.

The division is also involved in the development of novel
electromagnetic structures for use in microwave vacuum electronics
such as photonic band gap (PBG) structures and novel cathodes. We
have experimentally demonstrated the benefits of using PBG structures
in high gradient accelerators and high frequency microwave sources.

Our research encompasses a broad range of topics related
to high-intensity charged particle beams. One area of research that
we are currently investigating is that of periodically focused
intense charged-particle beams, which is useful in the study of
high-power microwave sources. We are also researching topics in chaos
and coherent structures in beams, and in particular, we are
analyzing the nonlinear dynamics of heavy ion beams for use in fusion
technology. Our group is currently working closely with the Waves
& Beams experimental group and with a number of other
universities in a MURI (Multidisciplinary University Research
Initiative) program to study the physics of vacuum electronics. We
have also extended our vacuum electronics research to include
an STTR on the investigation of crossed-field devices, e.g. the
magnetron. Finally, our group has been theoretically studying the
physics of small plasma toroids through a separate STTR program